The epoxidation of olefins is a reaction process that typically uses a catalyst, and heretofore, various heterogeneous and homogeneous catalysts have been used in processes for the epoxidation of olefins. Known catalyst art includes the use of a manganese (Mn) complex catalyst for epoxidizing olefins. For example, U.S. Pat. No. 5,329,024 discloses using a homogeneous 1,4,7-trimethyl-1,4,7-triazacyclononane manganese complex, [Mn2(TMTACN)2(μ-O)3](PF6)2.H2O, as a catalyst, for epoxidizing olefins with hydrogen peroxide (H2O2) as an oxidizing agent. “TMTACN” herein stands for 1,4,7-trimethyl-1,4,7-triazacyclononane.
One disadvantage of the above manganese complex catalyst is that such catalyst does not work well in epoxidizing olefins because the above manganese complex catalyst exhibits catalase properties and the catalyst is known to readily decompose H2O2 into water (H2O) and oxygen (O2). Therefore, the decomposition of H2O2 by the known catalyst reduces epoxide product yield. The catalytic epoxidation system disclosed in U.S. Pat. No. 5,329,024, if used on an industrial process scale, would necessitate an excess and inefficient use of H2O2.
The undesirable catalase activity exhibited by the above [Mn2(TMTACN)2(μ-O)3](PF6)2.H2O complex (abbreviated herein as “(TMTACN)Mn”) can be mitigated through the use of carboxylic acid additives. For instance, the use of the (TMTACN)Mn complex in conjunction with a carboxylic acid-grafted silica support can successfully epoxidize some specific olefins with more efficient utilization of H2O2. Turn over numbers (TON) of greater than (>) 600 are reached with the silica support, however, under identical acid-Mn ratios (e.g. >2:1), the homogeneous analogues of such catalysts produce less than (<) 65 TON (for example, as described in Schoenfeldt et al., J. Am. Chem. Soc., 2011, 133, 18664-18695). Unfortunately, the use of these known carboxylic acid-tethered mesoporous silica (TMTACN)Mn complex catalysts produces ring-opening diols as undesired byproducts. For example, when (TMTACN)2Mn2O3 is bound or tethered onto a solid support such as silica, cis-diols are produced as primary byproducts.
Ligand-tethered supports can also facilitate the epoxidation of olefins using (TMTACN)Mn complexes. For example, WO2000002872 discloses that a 65 percent (%) yield of styrene oxide is obtained through the use of a silica-tethered (DMTACN)Mn catalyst with a two-fold excess of H2O2. “DMTACN” herein stands for 1,4-dimethyl-1,4,7-triazacyclononane. For comparison, use of DMTACN in the absence of a ligand-tethered support produces only 5% yield of styrene oxide because of pronounced oxidant disintegration. WO2000002872 does not disclose the epoxidation of a divinylarene such as divinylbenzene (DVB). And, even though styrene and DVB are structurally similar, a catalyst capable of epoxidizing a mono-olefin such as styrene is not necessarily capable of epoxidizing a di-olefin such as DVB.
It is also known in the art that it is very difficult to obtain complete epoxidation of DVB to divinylbenzene dioxide (DVBDO) in an industrial process, because of the multiple terminal olefin groups present in DVB. Some of the multiple terminal olefin groups present in DVB are typically not fully converted to DVBDO using known epoxidation reaction processes; and therefore, an undesirable partially oxidized compound such as divinylbenzene monoxide (DVBMO) is generated. And, because DVBDO and DVBMO have similar boiling points, DVBDO cannot be easily separated from DVBMO except through very complex steps and costly separation operations.
Heretofore, a few catalytic epoxidation processes for the selective double epoxidation of DVB to DVBDO have been carried out with some degree of success. For example, WO2013070392A1 discloses a process for preparing a divinylarene dioxide by epoxidizing a divinylarene with H2O2 as the oxidizing agent and an iron-containing compound as the catalyst such that a yield of a divinylarene dioxide product of about 70% is obtained. However, the process disclosed in WO2013070392A1 uses a homogeneous catalyst and requires the addition of amine additives to achieve yields of about 70%.
U.S. Pat. No. 8,497,387 also discloses a catalytic epoxidation of a divinylarene with an oxidant in the presence of a catalyst and a solvent wherein the disclosed oxidant is a peroxycarboximidic acid. However, a peroxycarboximidic acid, used as an oxidant, generates stoichiometric amounts of amide organic byproduct waste, entailing multiple separation and purification steps to remove such waste. Thus, removal of the amide organic byproduct waste from the product produced using the process disclosed in U.S. Pat. No. 8,497,387 increases the complexity and cost of carrying out such process on an industrial scale.
It would advance the art of catalytic epoxidation of olefins to provide a catalyst or catalyst system useful for the epoxidation of an olefin reaction process that has low catalase activity; enhances epoxide selectivity, and increases reaction yield in the epoxidation of olefins. For example, the catalytic epoxidation of a divinylarene such as DVB to a divinylarene dioxide such as divinylbenzene dioxide (DVBDO) is a process that could be improved by using a catalyst that does not suffer from the aforementioned disadvantages of the currently known catalysts used in such a process.
In view of the above issues with the known prior art processes, it is desired to provide a novel catalyst composition and process for the catalytic epoxidation of olefins, such as a process for manufacturing DVBDO, that facilitates olefin dioxide formation in high yields (e.g., >70%) using low catalyst loadings (e.g. <5 mol %), while eliminating or at least mitigating: (i) the use of other additives and/or (ii) the generation of undesired byproduct waste.